1. Field of the Invention
The present invention relates to a dust-proof seal for a linear guide apparatus.
2. Description of the Prior Art
Generally, a linear guide apparatus includes, as shown in FIGS. 1-4, an axially elongated guide rail and a slider 2 movably mounted on the guide rail 1. The guide rail 1 has ball rolling grooves 3 formed in the outer surfaces of both side walls, and the slider, also, has ball rolling grooves (not shown) formed in the inner surfaces of side walls 4 so that the ball rolling grooves 3 of the guide rail 1, respectively, oppose the ball rolling grooves of the slider 2. A multiplicity of balls are rollably inserted between the opposing ball rolling grooves. The slider 2 moves on the guide rail 1 in the axial direction supported by the balls. As the slider 2 moves, the balls interposed the guide rail 1 and slider 2 roll and move to one end of a slider body 2A of the slider 2. Accordingly, in order to move the slider 2 continuously in the axial direction, it is necessary to circulate these balls. For this reason, ball return holes (not shown) are formed which penetrate the lateral side portion 4 of the slider body 2A in the axial direction, and at the same time, end caps 5 are provided at the front and rear ends of the slider body 2A and U-shaped connecting passages which are, respectively, in communication with the ball return holes are formed to thereby define ball circulating paths. Furthermore, since dust is deposited in the ball rolling grooves 3 and recessed path 6 of the guide rail 1 on which the slider 2 slidingly moves, and since smooth rolling of the balls and smooth movement of the slider 2 are impaired, usually, a dust-proof seal 10 is provided on the end cap 5.
As the prior art dust-proof seal 10, shown in detail in FIGS. 2 and 3 (Japanese utility model laid-open publication No. 60-103623), includes a metal plate 7 having both side edges bent to attach to the end cap 5, and a rubber member 8 adhered to the metal plate 7 and having protrusions slidably in contact with the ball rolling grooves 3 of the guide rail 1. The metal plate 7 is formed with an opening 9 to enable the guide rail 1 to pass therethrough, and the inner edge of the opening 9 is defined by straight lines. The metal plate 7 is essentially U-shaped. The rubber member 8 adhering to the metal plate 7 is provided with semi-circular protrusions 8a and 8b, and a trapezoidal protrusion 8c protruding inwardly at positions corresponding to the ball rolling grooves 3 and recessed path 6 of the guide rail 1.
Furthermore, at the tips of the protrusions 8a and 8b, and trapezoidal protrusion 8c, there are provided lip portions L (FIG. 4), which slide in the ball rolling grooves 3 and recessed path 6 to scrape dust and the like.
In such a dust-proof seal of the linear guide apparatus, the sealing property (the wiping of the dust deposited on the surface of the guide rail 1). is changed depending on the environmental conditions such as the size, shape, and the amount of dust, and the working conditions of the dust-proof seal itself such as non-uniformity of the size of component parts of the seal which affect the interference (negative clearance) for contact with the lip portions. Accordingly, in the prior art seal, for example, the wiping and the interference for contact have been adjusted by changing the size and shape of the dust-proof seal and the rubber hardness depending on the environmental conditions and working conditions.
However, when the lip portions are too hard, the sliding resistance is increased and the slide becomes unable to move smoothly. Also, any change in the size of the component parts of the seal will not be absorbed, and a gap will be formed between the lip end and the guide rail resulting in degradation of the sealing property. Conversely, when the lip portions are too soft, the wiping force is degraded, or the lip portions are caught by the edge of a hole of guide rail fixing bolt and the lip portions become reversed (turned over).
Furthermore, even when the hardness is within range, if the lip portions become worn after extended use, the required interference is no longer maintained, and the sealing property deteriorates.